Fluid filter assemblies with integral fluid seals

ABSTRACT

By making the fluid seal an integral part of either the filter element or the filter housing, the reliability of fluid filter assemblies is improved. In addition, the process for manufacturing filter assemblies and their individual components can be more easily automated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.09/014,488, filed Jan. 28, 1998, now U.S. Pat. No. 6,066,254 which is acontinuation of application Ser. No. 08/728,810, filed Oct. 10, 1996,now abandoned.

FIELD OF THE INVENTION

The present invention concerns fluid filter assemblies and assemblycomponents including a filter element, a housing and a fluid seal. Moreparticularly, the present invention concerns improved fluid filterassemblies and components in which the fluid seal is an integral part ofeither the filter element or the housing.

BACKGROUND OF THE INVENTION

Fluid filter assemblies are used in a wide variety of applicationsranging in scale from the industrial processing of liquids and gases tothe residential purification of drinking water. In general, such fluidfiltration devices are comprised of a filter element, a housing and afluid seal. The purpose of the fluid seal is to ensure that fluidentering the housing is directed through the filter assembly in apredetermined path, viz., through the filter element.

Traditionally, fluid seals are discrete parts, such as skirted gaskets,which engage the outer surface of the filter element and the innersurface of the housing. These seals are usually secured to the filterelement with an adhesive tape or an adhesive; see, for example, U.S.Pat. No. 5,389,260. The process for applying these seals tends to bevery labor intensive and suffers from the associated ergonomic, qualityand training implications. With the skirted gasket, fluid pressurebetween the skirt and the filter element tends to force the seal awayfrom the element, thus threatening the integrity of the seal. This isparticularly troublesome if the seal is secured to the filter element bytaping. Furthermore, the typically narrow width of a skirted gasketleaves the integrity of the seal susceptible to disruption by surfaceimperfections and particulate contamination. Yet another disadvantage ofthe taped-on seal is the tendency to fold back when inserted into thehousing, once again threatening the integrity of the seal and theoverall performance of the filter assembly. When the integrity of thefluid seal is compromised, the feed stream can bypass the filter elementand weaken the performance of the element. With reverse osmosiselements, such leakage results in ion rejection rates and permeate flowrates being less than optimal.

It would be desirable to have a fluid filter assembly whose productionmore easily lends itself to automation, particularly with respect to theincorporation of the fluid seal. It would also be desirable to have afluid filter assembly in which the integrity of the fluid seal was morereliable and less susceptible to damage or deformation duringinstallation and operation.

SUMMARY OF THE INVENTION

It has now been found that a filter assembly in which the fluid sealbecomes an integral part of the filter element or the housing reducesthe risk of the fluid seal folding back during installation andconcomitantly increases the reliability of the seal. In reverse osmosissystems, because of the increased performance and reliability of theseal, ion rejection is significantly improved. Furthermore, byincorporating the fluid seal as an integral part of the filter elementor the housing, the manufacturing process for the filter assembly andits constituent elements is more easily automated. Thus, the presentinvention concerns an improved fluid filter assembly of (a) a filterelement having an outer surface, (b) a housing having an inner surfacespaced from the outer surface of the filter element and (c) a sealbetween the outer surface of the filter element and the inner surface ofthe housing which directs fluid through the filter element, wherein theimprovement comprises the seal being an integral part of the outersurface of the filter element or the inner surface of the housing. Moreparticularly, the present invention concerns an improved fluid filterassembly of (a) a filter element, consisting of a cartridge filter ofgranular adsorbents or a hollow fiber or spiral wound membrane element,having an outer surface, (b) a housing having an inner surface spacedfrom the outer surface of the filter element and (c) a seal between theouter surface of the filter element and the inner surface of the housingwhich directs fluid through the filter element, wherein the improvementcomprises the seal being a material incorporated as an integral part ofthe outer surface of the filter element or the inner surface of thehousing.

Another aspect of the invention is a filter element in which a fluidseal is incorporated as an integral part of its outer surface. Yetanother aspect of the invention is a filter assembly housing in which afluid seal is incorporated as an integral part of its inner surface.When the fluid seal is incorporated into the housing, a seal is notrequired on the filter element and the cost of replacing the element isreduced. The fluid seal may also be incorporated as an integral part ofboth the inner surface of the housing and the outer surface of thefilter element. In this case, the entire filter assembly could bedisposable.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a spiral wound filter element 2 with two integral fluidseals 1 located near the ends of the outer surface.

FIG. 2 illustrates a filter assembly in which a spiral wound filterelement 2 with two integral fluid seals 1 has been inserted into ahousing 3.

FIG. 3 depicts a housing 3 with an integral fluid seal 1 adjacent to theend of the housing that accepts the filter element 2.

FIG. 4 shows a filter assembly in which the fluid seal 1 is an integralpart of both the inner surface of the housing 3 and the outer surface ofthe filter element 2.

DETAILED DESCRIPTION OF THE INVENTION

The fluid filter assemblies of the present invention are characterizedas having a filter element, a housing for the filter element and a sealfor directing the fluid through the filter element, the seal beingincorporated as an integral part of either or both the outer surface ofthe filter element or the inner surface of the housing. By “the sealbeing incorporated as an integral part of either the outer surface ofthe filter element or the inner surface of the housing” is meant thatthe seal is bonded to or adheres to the surface of the filter element orthe housing without the use of adhesive tape or a separate layer ofadhesive. The filter element itself and the cavity of the housing intowhich it is inserted are usually cylindrical in configuration. While thecylindrical shape is preferred for the filter element and the cavity ofthe housing in which it resides, other shapes are possible, such asthose of regular prisms, e.g., hexagonal prisms.

The fluid filter assemblies of the present invention can be used totreat a wide variety of fluids including both liquids and gases. Ofparticular interest is the treatment of water or brine, especially thepurification of drinking water in residential applications, e.g.,under-the-sink reverse osmosis units.

The filter elements, which comprise the functional element of the fluidfilter assembly, may be of any conventional design including cartridgetype filters used for granular adsorbents, i.e., charcoal or ionexchange or adsorbent resins, or hollow-fiber type or spiral-wound typeelements used for membranes, i.e., ultrafiltration or reverse osmosiselements. The outer surface of filter elements is typically comprised ofa plastic sheathing material, most often polyethylene (PE),polypropylene (PP) or polyvinyl chloride (PVC) in the form of a tape orfilm. In high pressure applications, fiber glass reinforced plasticslike epoxy resins can be used to provide improved safety performance.

The housing into which the filter element is inserted has an inlet forthe feed, an outlet for the filtrate or permeate and, in the case of ahollow fiber or spiral wound membrane element, an outlet for thedischarge of the retentate. FIG. 2 illustrates, in part, a typicalhousing 3 for a spiral wound reverse osmosis filter element with a feedinlet 4, a permeate outlet 5 and a retentate outlet 6. The inner surfaceof the housing is typically comprised of a plastic material, most oftenacrylonitrile-butadiene-styrene (ABS), PVC, PE, PP, polysulfone,polystyrene (PS) or fiberglass reinforced epoxy resin, or a metal, suchas aluminum or stainless steel.

The seal or gasket between the outer surface of the filter element isand the inner surface of the housing serves the following functions: (a)separating the cavity containing a liquid to be filtered from the cavitycontaining the filtrate in the case of a cartridge filter or from thecavity containing the retentate in the case of a hollow fiber or spiralwound membrane element; and (b) holding the filter element in place inthe presence of a pressure differential. The gist of the presentinvention is the incorporation of the seal as an integral part of eitherthe outer surface of the filter element or the inner surface of thehousing.

To accomplish the above functions, the material from which the seal isfabricated must remain flexible and resilient. To become an integralpart of the filter element or the housing, the seal material must be onewhich can be easily applied and affixed to the surface of the filterelement or housing without the need of an adhesive tape or an adhesive.Suitable seal materials can be either thermoplastics, i.e., polymerswhich soften when exposed to heat and return to their original conditionwhen cooled, or thermosets, i.e., polymers which solidify irreversiblywhen heated. Thermoplastics and thermosets such as ethylene-propylenediene monomer (EPDM), neoprene, buna rubbers, ethylene-vinyl acetate(EVA), PE and PP are suitable seal materials and can be molded directlyonto the surface of either the filter element or the housing. Even morepreferred are polyurethane and silicone materials which can be appliedwith or without a mold and can be cured at relatively low temperatures,for example, H. B. Fuller's PURFORM™ foamed-in-place products.

Some of the seal materials may be applied as foams, which is oftenpreferred. Air or an inert gas such as nitrogen or carbon dioxide can beintroduced with the seal material to produce a foamed seal.Alternatively, the gas can be chemically generated in situ, e.g., duringthe production of polyurethane, and carbon dioxide is generated byadding water to the isocyanate.

The seal material, particularly polyurethane, can be integrally attachedor affixed to the filter element or the housing by means of injectionmolding or by means of spin or rotational casting, i.e., the controlledapplication of the seal material to a rotating filter element orhousing. Both processes are well known in the art and can beconveniently automated. See, for example, the following references: B.Baumberger et al., “Automatic Placement of In-Situ Foamed Gaskets”,Polymer Processing Machinery 4, Conference Proceedings, PRI Processingand Engineering Group, Bradford University, Jul. 3-4, 1991, p.12/1-12/10; Spuehl Plastics Machines, publication of Spuehl AG, 1990; A.Von Hassell, “Urethane Equipment”, Plastics Technology, May, 1985, p115-6; M. S. Coons et al., “Rotational Casting of PU Covered Rolls”,Rubber World, 210, No. 1, April, 1994, p 28; R. Sprey, “FabricationMethods for Solid Polyurethanes”, Rubber World, 182, No. 1, April, 1980,p 32; Foamed-in-Place Products, publication of H. B. Fuller Company,1994; and Introducing PURFORM™ Foam-in-Place Materials to YourOperation, publication of H. B. Fuller Company, 1995.

With injection molding, a hollow mold or molds of appropriateconfiguration are clamped or secured to either a filter element or ahousing and the thermoplastic or thermoset seal material is injectedinto the mold and cured. A material that promotes release of the moldmay optionally be applied to the surface of the mold. After curing iscomplete, the molds are removed. With the injection molding technique,the fluid seal can be incorporated as an integral part of both thehousing and the filter element by orienting the element in the housingand using the inner surface of the housing and the outer surface of theelement as part of the mold.

With the controlled application method, the filter element or housing isrotated while the seal material is applied through a nozzle. Thedimensions of the seal are controlled by such factors as feed rate ofthe seal material, rotation rate of the filter element or housing, angleof the nozzle and the temperature and rate of cure. Such factors aredependent upon the composition of the particular seal material employedand can be ascertained by routine experimentation.

In some instances, in order for the fluid seal to become an integralpart of the filter element or the housing, it may be necessary topretreat the outer surface of the filter element or the inner surface ofthe housing to remove, for example, a peel-off coat. Such a pretreatmentmay include but is not limited to heat treatment, corona, abrasion oracid etching.

In yet another embodiment of the invention, the seal is rendered“integral” with the outer surface of the filter element by applying ashrink wrap covering over the outer surface of the filter element andseal. For example, the seal may be positioned about the outer surface ofthe filter element and then fixed thereto by applying a conventionalshrink wrap material about the outer surface of the filter element andseal, thereby fixing the relative position of the seal with respect tothe outer surface of the filter element. The shrink wrap material maycover the entire surface of the filter element or only the portion ofwhich where the seal resides. In either case, the shrink wrap materialmust remain flexible enough to permit the seal to flex, i.e., compressand expand, in response to pressure applied thereto. That is, the sealmust be capable of compressing when the filter element is inserted intoa corresponding housing, thereby engaging the inner surface of thehousing and providing a seal between the housing and filter element.Applicable shrink wrap materials and their application are well known inthe art. Preferred materials including a Type A durameter of about 30 to80 in order to permit the seal to properly flex. The seal material usedin connection with the shrink wrap material includes both foam andnon-foam materials (e.g., thermoplastics, thermosets) as previouslydescribed. These seal materials may be applied in a manner so as toindependently form an integral seal with the outer surface of the filterelement prior to the application of the shrink wrap material. However,in several embodiments of the present invention, the seal member doesnot form an independent integral seal with the filter element. That is,the seal member may be movable relative to the outer surface of thefilter element. For example, the seal member may comprise a pre-formedo- ring configuration or a foam o-ring type configuration which thefilter element is inserted into. The seal member is rendered integralwith the filter element by application of shrink wrap material over theseal and filter element.

The exact configuration of the integral seal is not critical and canvary widely, i.e., a single band of a width of about 0.1 to about 6inches, a single band extending the entire length of the outer surfaceof the filter element or the entire length of the inner surface of thehousing, multiple bands of a width of about 0.1 to about 3.0 inches,etc. In several embodiments, multiple bands of a width of about 0.5 toabout 2.0 inches are preferred. The height of the integral seal isdetermined by the clearance between the outer surface of the filterelement and the inner surface of the housing and should provide for asnug and reliable fit of the filter element in the housing. The sealscan be beveled to facilitate the insertion and the extraction of thefilter element into or out of the housing. Placement of two integralseals near the termini of the filter element or the housing facilitatesstability of the filter assembly. FIGS. 1 and 2 illustrate a spiralwound filter element 2 with two integral fluid seals 1 located near thetermini of the element and a filter assembly in which the filter element1 has been inserted into a housing 3, respectively.

In a typical example of the spin casting or rotational casting method,the filter element or housing is rotated at an experimentally determinedspeed while the components of the seal material and, if desired, air, aninert gas or precursors which will chemically generate an inert gas arefed into a computer controlled nozzle which applies the seal material tothe surface of the rotating element or housing.

In a typical example of the injection molding method, a mold is clampedto the filter element or housing and the components of the seal materialand, if desired, air, an inert gas or precursors which will chemicallygenerate an inert gas are injected into the mold. After curing, the moldis removed.

The following examples further illustrate the invention.

EXAMPLE 1

Rotational Casting

A FILMTEC™ TW30-1812-36 spiral wound reverse osmosis filter element,which has a polypropylene outer surface and which has been wound andfinished to the point where the addition of the brine seal is the onlystep remaining, is placed in a fixture that rotates the element aboutthe axis of the product water tube. A polyol component (a), containingethylene glycol, carbon black, silica and enough water to producesufficient carbon dioxide in situ to provide a foamed product uponreaction with the isocyanates, and an isocyanate component (b),containing methylene diphenyl isocyanate (MDI), are metered continuouslyat ambient temperature with high precision into a mixing head and nozzleat a stoichiometric ratio of MDI to the total of ethylene glycol andwater and at a rate designed to dispense a predetermined distribution offoamed-in-place polyurethane material on the surface of the element. Theelement is rotated at a predetermined speed while a robot dispenses thefoamed-in-place polyurethane material from the nozzle to the surface ofthe rotating element to which it adheres. The nozzle is moved axiallyalong the element while the material is dispensing to achieve apredetermined distribution of foamed sealant. The amount of material atany point of the surface of the element is a function of the relativemotion of the rotating element and the dispenser nozzle and the flowrate of the foamed polyurethane material. After the appropriate amountof material has been dispensed in the desired pattern, the element isremoved from the rotating fixture and allowed to cure at ambienttemperature.

EXAMPLE 2

Injection Molding

The same materials and elements as used in Example 1 are used in thepresent example. However, rather than applying the seal by spin orrotational casting, the foamed polyurethane material is applied byinjection molding. The element is placed in an aluminum mold coated withTeflon™ polymer that is sized for the element and contains a void spacedefined by the contour of the filter element and the integral brineseal.

The foamed polyurethane material is injected into the mold using thesame robotic assembly of Example 1 which engages the dispensing nozzleto a port in the mold which allows the material to be introduced intothe mold once it is closed. After the brine seal material has cured, theelement with its molded on brine seal is removed from the mold.

EXAMPLE 3

Test Method for Spiral Wound Reverse Osmosis Elements

Dry filter elements of 1.8 inch nominal diameter having standard tape-onbrine seals or having foamed-in-place brine seals as in Example 1 areinserted into 2 inch inside diameter test vessels of a standard reverseosmosis system. The system is then operated under standard testconditions of approximately 50 pounds per square inch gauge pressure, 15percent recovery and 25° C. for 30 minutes with feed water containingabout 485 parts per million sodium bicarbonate. At the end of 30minutes, a sample of the permeate is withdrawn and the conductivity(micromhos) and volume flow rate are determined. Permeate flow (gallonsper day) and rejection (%) are calculated and normalized to allowcomparisons of element performance. The results are summarized in TableI.

TABLE I COMPARISON BETWEEN FOAM-IN-PLACE (FIP) AND TAPE-ON (TAPE) BRINESEALS Con- ductivity (μmho) Rejection (%) Flow (gal/day) TAPE FIP TAPEFIP TAPE FIP 19.8 15.7 96.4 97.2 54.1 50.6 20.6 18.2 96.3 96.7 54.4 54.321.6 14.8 96.1 97.3 54.4 52.2 21.5 15.5 96.1 97.2 53.4 52.4 19.8 16 96.497.1 53.2 53.3 18.5 16.3 96.6 97.0 54.5 54.8 20.6 16.2 96.3 97.1 54.153.9 20.4 15.5 96.3 97.2 54.9 53.9 18.2 16.5 96.7 97.0 53.7 54.7 18.5 1696.6 97.1 53.4 52.8 16.5 16.6 97.0 97.0 51.7 53.4 22.7 16.6 95.9 97.054.5 55 19.3 16 96.5 97.1 55.3 54.4 19.8 17.1 96.4 96.9 54.7 55.2 18.814.9 96.6 97.3 54.6 54.4 16.7 97.0 54.3 16.2 97.1 55 18.2 96.7 55 17.296.9 55.7 17.8 96.8 55.2 AVERAGE: 19.77 16.40 96.40 97.02 54.06 54.03Stdev: 1.56 0.95 0.29 0.18 0.88 1.26

What is claimed is:
 1. A filter element comprising a cartridge filter ofgranular adsorbents or spiral wound membrane element, having an outersurface and a foam seal incorporated as an integral part of the outersurface.
 2. The filter element of claim 1 wherein the filter element isa spiral wound membrane element.
 3. The filter element of claim 2wherein the integral seal is comprised of a foamed polyurethanematerial.
 4. The filter element of claim 3 wherein the integral sealcovers substantially the entire length of the outer surface of thefilter element.
 5. A filter housing adapted for receiving acorresponding filter element, wherein the housing includes an innersurface and a foam seal incorporated as an integral part of the innersurface, wherein the seal is adapted to contact with an outer surface ofa corresponding filter element.
 6. The filter housing of claim 5 whereinthe seal is comprised of a foamed polyurethane material.
 7. A filterelement comprising a cartridge filter of granule adsorbents or spiralwound membrane element having an outer surface, a seal positioned aboutat least a portion of the outer surface, and a shrink wrap materialcovering the seal and outer surface of the filter element.
 8. The filterelement of claim 7 wherein the seal is a foam material.
 9. The filterelement of claim 8 wherein the seal covers substantially the entirelength of the outer surface of the filter element.
 10. A filter elementhaving an cylindrical outer surface extending between two ends, a sealcomprising a single band disposed about the outer surface of the filterelement and which extends between the ends of the filter element andalong substantially its entire length, and a shrink wrap materialdisposed over the seal.
 11. The filter element of claim 10 wherein thefilter element comprises a spiral wound filter element.
 12. The filterelement of claim 10 wherein the seal comprises a foamed material. 13.The filter element of claim 10 wherein the seal comprises a non-foamthermoplastic or non-foam thermoset material.
 14. A filter housingadapted for receiving a cylindrically shaped filter element, wherein thehousing includes a corresponding cylindrically shaped inner surfacewherein the improvement comprises a foam seal incorporated as anintegral part of the inner surface, wherein the seal is adapted tocontact with an outer surface of the corresponding filter element.